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10th Planet

Possible 10th and 11th Planet-Like Objects Orbiting the Sun
ExploreZone, 7 October 1999

After studying 13 comets whose orbits seem to have been affected by a massive object far beyond Pluto, a British scientist announced today that there may be a previously unknown and very large planet orbiting the Sun. Separately, three astrophysicists are set to propose that a brown dwarf lurks in the outer reaches of our solar system. Brown dwarfs are near-stars that never gathered enough fuel to become true stars; they can be many times more massive than Jupiter. If either object is confirmed to exist, researchers will have a whole new batch of theories to create about how comets are formed, how they evolve, and how some are set on devastating paths toward Earth.

The two studies combined also open the possibility that a host of unfound planet-like objects may one day be added to our current nine-item list. John J. Matese, a physics professor at the University of Louisiana, writes of the possible brown dwarf, based on a study of 82 comet trajectories, in an upcoming issue of the journal Icarus. Matese told that it's "very plausible" that there are several unknown planets and/or brown dwarfs orbiting the Sun. "We suggest that this (brown) dwarf may only be the most likely to be detected during this epoch," Matese said, adding the cautionary note that "the existence of the object we discuss is not certain." The brown dwarf would not likely have formed from the disk of gas and dust out of which the other planets were born, Matese and his colleagues say.

The possible 10th planet
Writing in the Oct. 11 issue of the Monthly Notices of the Royal Astronomical Society, Open University professor John Murray says he observed 13 long-period comets - objects that orbit the Sun but also travel to the far reaches of the solar system - whose trajectories follow a similar arc. Murray suggests the common path is the result of a gravitational deflection caused by a planet-like object at least as massive as Jupiter. Interestingly, Murray told that his research had been done in 1996, rejected by two science journals, and only recently been accepted for publication. "It was finally accepted by the Monthly Notices of the Royal Astronomical Society in May this year, but was still not really taken very seriously until a few days ago, when (Matese's team) announced that they have come to a very similar conclusion."

Murray describes his planet-like object as a lone wanderer that has been captured into an orbit around the Sun after a journey through space. Its orbit, he says, is in the opposite direction as the nine known planets (a motion called retrograde). He says the object orbits the Sun 32,000 times farther away than Earth (some 3,000,000,000,000 miles from the Sun) where it would be extremely faint and slow moving, and so could have escaped detection by present and previous searches for distant planets. He estimates the object takes 6 million years to orbit the Sun. ...
Possible brown dwarf
If Murray's proposed object were several times more massive than Jupiter, it could possibly be a brown dwarf, a massive star-like object that fell just short of the required mass and energy to stimulate stellar processes. Still, brown dwarfs are huge, and Murray argues that if the object that seems to be deflecting comets were a brown dwarf, it is more likely it would have been detected already. Matese, the University of Louisiana professor who proposes there is a brown dwarf out there, did similar research on comets from the Oort cloud. Matese calls the possible brown dwarf a companion to the Sun. He estimates its mass at three times that of Jupiter and puts it at 25,000 AU from the Sun (roughly in the middle of the range of Murray's estimate.)

In the analysis of highly accurate orbits of 82 Oort cloud comets, Matese and his colleagues detected a pattern connecting the orientation and shape of a comet's orbit path. They suggest that this can best be explained if there is an object approximately 3 times as massive as Jupiter orbiting in the vicinity of Oort cloud comets. Matese says he can't predict the object's exact location, but says it is potentially observable by radio telescopes and next-generation infrared telescopes. He told that it is possible that his brown dwarf and Murray's possible planet are in fact the same object, but that he had not yet studied Murray's results thoroughly. At an Oct. 11 meeting of the American Astronomical Society in Italy, Matese and his colleagues will explain that if the brown dwarf is confirmed to exist it will "play a major role in our understanding of how comets get into the Oort cloud and how they return. Comets from the Oort cloud are important contributors to the impact history of the Earth and are often claimed to be the cause of mass extinctions like the one in which the dinosaurs, and many other species, disappeared from the fossil record 65 million years ago."
What's next?
Before either object might be added to any lists, it would have to be observed directly. "It needs to be confirmed by pictures taken with the largest telescopes on Earth," Murray said of his possible planet. "The problem is that it will be very faint (about 10 million times fainter than the faintest star visible to the naked eye) and will move very slowly, so two photographs taken about six months apart would be best to show the movement, though most of the movement would be due to the Earth moving in its orbit. There is also a big area to search, as there is a good bit of uncertainty in its predicted position."